The use of metering rod type coaters for applying coating, for example to the surface of a size press are well known. U.S. Pat. No 4,250,211 issued Feb. 10, 1981 to Damrau, U.S. Pat. No. 4,706,603 issued Nov. 17, 1987 to Wohlfeil and U.S. Pat. No. 5,078,081 issued Jan. 7, 1992 to Kustermann, all disclose short dwell coaters with metering rods defining one side of the main coating or metering outlet from the coating head that could be used to apply coating to a web directly onto the surface of a roll of a size press coater or the like.
It is also known to use grooved rods which have contoured peripheral surfaces and function as volumetric metering rods to meter the amount of coating applied, i.e. the surface of the rod is defined for example by winding small diameter wire helically about the rod to define the rod surface or by machining circumferential grooves formed in the rod. The diameter of the fine wire defines gaps or grooves between the convolutions of the helix. The size of these gaps as defined by the diameter of the fine wire plays a significant role in controlling the amount of coating that will be applied.
Canadian patent application 2,040,845 published Oct. 20, 1991, inventor Rantanen, discloses a rod coater that utilizes a metering rod having a very smooth peripheral surface and that is rotated contrary to the direction of movement of the coating through the coating outlet.
In all of the above described systems, uniformity of coating application may be deficient. The type of metering rod that is used i.e. grooved or smooth, imparts an upper limit to the solids content of the coating that may be properly applied.